Bob Widlar was a brilliant and eccentric designer of linear integrated circuits who worked for Silicon Valley. He was also a practical joker. One circuit he created became known as the "hassler." A colleague, engineer Robert A. Pease, remembers:

One of the celebrated things Widlar did was to put a "hassler" in his office. When a person came in to his office and spoke loudly, this circuit would detect the audio, convert the audio to a very high audio frequency, and play back this converted sound. The louder you talked, the lower the pitch would come down into the audio spectrum, and the louder it would play. So if you really hollered, it would make sort of a ringing in your ears. Of course, if you noticed this "ringing" in your ears, and stopped for a while to listen, the "hassler" circuitwould shut up. He gradually got people to stop yelling at him. I mean, Bob really was almost always a soft-spoken person. He didn't have to yell or shout to get his message across. When he did speak, and softly at that, people would soon realize that it was a good idea to listen to him...

One night Bob left the "hassler" on. The next morning, his secretary tried to do some typing, and every time she hit a key, the "hassler" would chirp. It drove her nuts until Widlar came in and turned it off.

Mr. Pease tried to replicate the circuit but couldn't find any record of it, so he built his own. If you're electronically gifted, you might be able to build one for yourself from the description below, from a 1999 Electronic Design magazine:

Here's how it works: The tiny microphone should sit on your desk, aimed to pick up sounds from a visitor. The small audio signal goes through just a couple feet of twisted pair, to a preamplifier A1, and a bunch of stages of low-pass filter. We want to make sure that it responds only to audio signals below a couple kilohertz. Next comes a second amplifier A2 with adjustable gain per P1 (the output's dc level is still about 3 V dc). Then the rectified output is amplified by A3, with an adjustable offset provided by P2. A3's output is inverted by A4, and both the inverted and direct are fed to a voltage-controlled oscillator A5. This is set to run at 24 kHz when there's no audio signal. When loud audio is present, the frequency can come down to 14 kHz or even to 12 kHz--but no lower. The output of A5 is just fed through a couple of dumb emitter followers to drive a speaker. This provides the nasty noise you hear if someone talks too loud. In concept, you could design this to be low powered for battery operation by turning down the amplitude of the highfrequency output when there's no significant audio input. But, realistically, that's more trouble than it's worth, so you might as well use a 12-V (adjustable) linepowered supply rated at more than 100 mA. You won't use this very often, and you probably won't use it very long, so a simple rig with 12 V dc makes sense.